Conversion of information contained on a surface into an electrical signal can be achieved in number of ways.
In one arrangement relative movement is effected between a spot of light and an information bearing surface and reflected light from the spot is focussed onto a photocell. As the spot moves over the surface, the reflected light level varies in relation to the information content and a varying electrical signal derived from the photocell comprises the electrical video signal.
In another arrangement an electron beam is scanned over a photoconductive surface onto which an image of the surface is focussed. The electron beam current varies with the light level at different points of the photoconductive surface and an electrical signal derived from these current variations comprises the said electrical video signal.
In a further arrangement a narrow band of an illuminated information bearing surface is focussed onto a line of photoelectric elements, which are addressed in sequence and produce an electrical signal a parameter of which (such as amplitude) varies with the light level falling on the individual elements as the latter are scanned. By moving the lens and photoelectric elements relative to the illuminated surface, the latter is scanned in a series of parallel bands, each of which is effectively "scanned" by the sequential addressing of the elements.
Other arrangements are possible, it being understood that the foregoing are only exemplary of the large number of different types of device which can be used as a scanner.
Irrespective of the scanning method employed it is usually a prerequisite that the information bearing surface to be scanned is flat and conventionally a flat support is provided on which a document can be laid out flat and, where necessary, a transparent sheet such as a sheet of glass is laid over the document so as to maintain the latter flat. Alternatively the document may be laid face down on a window typically formed from a sheet of glass and if required a backing marker is laid over the document so as to maintain the latter flat in contact with the window.
Where the document to be copied is a book, the latter may be laid out flat with the page(s) to be copied flattened for example against a window through which the page(s) is/are to be viewed. However, it is found that the flattening of a book in this way can cause the binding of the book to be damaged. Where old and valuable books are to be scanned, opening the book out and flattening the page(s) to be scanned can easily damage the book and it is an object of the present invention to provide a document scanner for scanning the pages of a book without damaging the binding of the book.
One arrangement which has been proposed to overcome this problem comprises a wedge shaped support of transparent material such as glass over which the book is inverted. By employing a wedge angle of approximately 90.degree. a book can be fitted over the wedge with minimal strain on the binding. However two problems have been discovered in practice, namely:
(1) the book is upside down during scanning and has to be lifted up and possibly turned over to enable another pair of pages to be selected. This results in excessive handling of the book which can provie almost as damaging as if the book is flattened and can produce operater fatigue.
(2) the book is suspended during scanning over the sharp apex of the wedge under its own weight and where the weight of the book is sufficient to keep the pages flat against the sides of the wedge, the weight can cause damage to the binding.